1. Field of the Invention
The present invention relates to a wireless communication system, and more particularly, to a management procedure in a wireless communication system associated with a location service and a station supporting the management procedure.
2. Description of the Related Art
With development of information communication technologies, a variety of wireless communication technologies have been developed. A wireless LAN (WLAN) is a technology permitting wireless access to Internet in specific service areas such as home or companies or air planes by the use of portable terminals such as a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP) on the basis of a radio frequency technology.
These days, thanks to the increased availability of WLANs, portable terminal users such as laptop computer users are able to perform their tasks with increased mobility. For example, a user can take his laptop computer from his desk into a conference room to attend a meeting and still have access to his local network to retrieve data and have access to the Internet via one or more modems or gateways present on the local network without being tethered by a wired connection. Similarly, business travelers commonly use their portable terminals to gain access to their email accounts, to check if there is any unread email, and to read and send email.
In the initial WLAN technology, a data rate of 1 to 2 Mbps was supported by the use of frequency hopping, spread spectrum, and infrared communication using a frequency of 2.4 GHz in accordance with the IEEE 802.11. In recent years, with the development of the wireless communication technology, 54 Mbps in maximum can be supported by applying the orthogonal frequency division multiplex (OFDM) technology, etc. to the WLAN. In addition, the IEEE 802.11 has developed or is developing wireless communication technologies for improvement in quality of service (QoS), compatibility of an access point (AP) protocol, security enhancement, wireless resource measurement, wireless access in vehicular environment, fast roaming, mesh network, inter-working with external networks, wireless network management, and the like.
Among the wireless communication technologies, the wireless network management is designed to allow stations (STAs) or access points (APs) to collect information on wireless networks, to diagnose problems, or to provide protocols associated with procedures for providing services other than data transmission. For example, the wireless network management in a wireless LAN provides protocols associated with an event request and report procedure, a diagnostic request and report procedure, a location service procedure, a basic service set (BSS) transition management procedure, a flexible broadcast multicast service (FBMS) procedure, a traffic filter service (TFS) procedure, a sleep mode request and response procedure, and the like.
The location service procedure or a simple location procedure includes a protocol for the wireless network management for providing presence information or STA location information, such as accessibility, availability, and/or interactions of a portable terminal at a specific time. In general, the presence information means information on a state of a portable terminal at a specific time, means for making a communication between users, an intention for communication, capability at the time of communication. The location information includes information required for allowing a STA to find out its location, other than information directly indicating a location of a STA.
However, the discrimination of the presence information and the location information is arbitrary and the information pieces may be incorporated into any one in accordance with a network management protocol of a wireless communication system. For example, the wireless network procedure relating to a location service in a wireless LAN system includes a communication protocol for transmitting both the presence information and the location information. Accordingly, the location service procedure or the location procedure in the following description includes all the protocols for acquiring or providing radio information associated with a portable terminal or a base station, location information, and motion information.
In a wireless communication system, location information of a portable terminal which can be acquired by the use of a management procedure of a location service serves as basic information for providing the location service such as an emergency service to a user or efficiently managing a wireless communication system. The location information of a portable terminal in an environment where a global positioning system (GPS) is not installed or cannot be utilized (for example, in a building) can be acquired by the use of another terminal knowing the location. For example, when a distance to another portable terminal or a base station knowing the location can be acquired, information on the correct location of the portable terminal can be acquired using a trigonometrical survey.
A distance between two portable terminals or between a portable terminal and a base station communicating with each other can be acquired using a time until a transmission signal arrives, that is, a propagation delay time of a signal. However, since a communication is made in a relatively narrow area in a wireless LAN environment and the propagation speed of a signal is close to the light speed, it is very important to knowing accurate location information that the propagation delay time should be acquired accurately in a very minute unit such as a nano-second unit or less. In this case, a signal processing time in the portable terminal or the base station can affect acquiring the accurate propagation delay time even if it is very short, thereby greatly affecting the accuracy of the location information.